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Big Bang Background Radiation Question

  1. Jan 16, 2015 #1

    I have a simple question that will probably have a simple answer.
    If the Big Bang was a finite event (i.e. took place over a certain amount of time) why is it that the background radiation from it as sensed on Earth (TV static) is continuous? Will it continue to be continuous forever? How is this possible if the radiation coming from it was a single, finite event?

  2. jcsd
  3. Jan 16, 2015 #2


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    It was finite in time, but happening over a large (possibly infinite) volume of space. We're getting CMBR from farther and farther away every instant.
    The expansion of space is, however, continuously stretching the radiation, so it's not continuous in that sense (its energy goes down).
  4. Jan 18, 2015 #3


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    The cosmic microwave background did not directly come from the big bang any more than you or I did, though you may read otherwise in some places. It was created about 370,000 years after the big bang during an event called 'recombination'.


    The idea is that the entire universe was filled with a very hot plasma. Well, hot plasma radiates thermal radiation, which includes visible light. Once recombination occurred, it was like a fog lifting from the universe. The plasma turned into a neutral gas, which doesn't absorb light, so there was nothing to block the light from propagating. The CMB is this thermal radiation. It has been redshifted so much it is now out of the visible range and into the microwave range.

    The radiation reaching us now was emitted further away from us than the radiation that reached us one second ago, and that was emitted further away than the radiation that reached us 2 seconds ago.
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